Edge Of Hole Research Articles

Influence of Spatial Characteristic Parameters of Film Cooling Holes on the Strength of Turbine Blade

In order to improve the fatigue resistance of turbine blades with special-shaped film cooling holes in real working environments, the spatial geometric characteristics of the gas film holes are studied by using the numerical calculation method of gas-thermal-solid depth coupling, which is based on the spatial geometric characteristics of special-shaped film cooling holes. Then, the influence of stress level and durable strength at the hole edge is developed, which includes the parameters of the film jet angle, the flow direction divergence angle, the span-wise divergence angle, and the pore diameter on the film cooling holes. The results show that the flow direction expansion angle and the spanwise expansion angle are the most significant impacts on the hole edge stress at the same pore diameter and film jet angle. Compared with the cylindrical gas film hole, it is decreased by about 9.3% to 25.8%, which is the hole edge equivalent stress of the special-shaped gas film hole. The durable strength of the hole edge increases by about 11.1% to 25.2%.

Experimental investigation of nanosecond laser Machining of 3D printed carbon fiber reinforced polymer (CFRP) composite

Carbon fiber reinforced polymer (CFRP) composites are widely used in automotive and aerospace applications due to their high specific strengths, high fatigue and creep resistance, and excellent corrosion resistance. Additive manufacturing (AM) or 3D printing has opened new ways of manufacturing complex 3D parts using CFRP composites. As a result, researchers have gained interest in the machining or post-processing of 3D-printed CFRP composites. This study aims to investigate the feasibility of using a nanosecond laser for machining single craters or blind holes and slots on 3D printed CFRP samples and understand the effects of important process parameters on feature dimensions, (i.e., crater diameter, slot width, crater/hole depth, and slot depth), heat affected zone (HAZ), and surface quality of the machined features. A 1064 nm wavelength laser system with a focal length of 160 mm was used, whereas the number of pulses, laser energy level, and back-and-forth laser passes are varied. The heat-affected zone is found to be influenced by the laser energy level as compared to the number of pulses. It is found that for the same number of pulses, there is a clear sign of an increase in HAZ with the increase in laser energy level. With the increase in the number of pulses, the hole or slot edge becomes more defined and clearer, whereas the HAZ is mostly determined by the energy level. There is an accumulation of molten or removed materials at the edge of holes or slots causing jagged edges of machined features, which gradually diminishes when the edge becomes smoother for a higher number of pulses, or accumulated materials evaporate away at the higher setting of energy level. Finally, it is found that the nanosecond laser system is capable of machining quality holes and slots on the 3D-printed CFRP composite. To obtain features with well-defined profiles and minimal heat-affected zone, an understanding of the effects of laser process parameters is important.

Interaction between peptides and an MoS2 monolayer containing a nanopore: First-principles calculations

• The reaction between small peptide molecules and the MoS2 nanopore are explored: • Serine and Glycylglycine don't have any bonding and interaction with MoS2/NP. Each plays the role of a passer in the system. • Two dipeptides, Aspartame and Carnosine, and the tripeptide Glutathione react with Mo and S atoms surrounding the hole and form stable compounds. First-principles density functional theory (DFT) is employed to explore the interaction between a peptide molecule and two-dimensional (2-D) monolayer of molybdenum disulfide (MoS 2 ) containing a nanopore. A variety of monopeptides, dipeptides and also a tripeptide are individually positioned in the hole of a MoS 2 layer and the overall electronic structure calculated. The results indicate that bonding occurs between some molecules and the hole edge. The outcome of reaction can be predicted through the potential energy surface. These results strongly suggest that 2-D MoS 2 nanopores have a wide range of biological applications and deserve further exploitation by experiment.

Medico-legal study of the hymen

BackgroundThe study of hymen morphology and injuries is critical in forensic medicine, particularly in Iraq and other Asian countries. Problems with the hymen can have serious social consequences. Aim of the studyThe aim of this study is to shed light on various hymen's variants, as well as the possible causes of their injuries and their medicolegal significance. MethodThis study was carried out at Baghdad's medico-legal directorate (M.L.D.) from January 1st to March 31st, 2017. There were 127 cases in total. They ranged in age from two to sixty. The morphology of the hymens, their injuries, and other relevant details were documented using a specific questionnaire. ResultsCompared to other varied examinations undertaken, such as infertility, impotence, and others, the examination of the hymen made up (5.1%) of all examinations conducted in the Medico-Legal Directorate (M.L.D.) clinic in Baghdad. The majority of the women tested were over the age of 14. The annular hymen was the most common variant (57.3%). The elastic hymens percentage was 14.6% while the Imperforated variant had the lowest prevalence (0.8%). The majority of the properties of the examined hymens were smooth free edge, medium consistency, and medium sized hymen opening. The majority of the cases involved female children (prepubertal girls) who were accidently injured, followed by sexual assaults and wedding night doubts. The majority of hymen tears (40.2%) were old. Multiple tears (47.5%) outnumbered single tears (37.3%). Fresh tears were only observed in adult girls. ConclusionThe annular variant of the smooth free edge, average consistency, and average hole size is the most common hymens. The elastic hymens were a main reason for the referral of cases for medical examination due to wedding night doubts. In more than half of the cases, the hymens were smooth with no transection or deep notches.

An analytic solution of an arbitrary location through-crack emanating from a nano-circular hole in one-dimensional hexagonal piezoelectric quasicrystals

The mode III fracture performance of an arbitrary location through-crack at the edge of a nano-circular hole in one-dimensional hexagonal quasicrystals is studied. Based on the G-M elasticity theory, the piezoelectric quasicrystal theory and the boundary value problems theory, the phonon, phason and electric fields of the nano-defects (nano-hole and nano-cracks) are obtained, and the analytic expressions of the field intensity factors at both ends of through-crack are present. The present solution can be degenerated into the existing results. The relationship between the field intensity factors with the nano-defects related parameters, far-field loads and piezoelectric quasicrystal coupling coefficient are discussed. The field intensity factors have obvious size effects when the defects size is at nanoscale and the surface effect is considered. The field intensity factors tend to be classical theory with the increase in defect size. The field intensity factors show different changes with the increase in crack location angle and relative size between cracks. The size effect of the field intensity factors is significantly affected by the crack location. The far-field mechanical-electric loads and the piezoelectric quasicrystal coupling coefficient have obvious influence on the field intensity factors.

Experimental Assessment of Hole Quality and Tool Condition in the Machining of an Aerospace Alloy

This paper deals with an experimental investigation of hole quality in Al2024-T3, which is one of the aerospace alloys used in aircraft fuselage skin due to its high level of resistance to fatigue crack propagation. The experiments are conducted with 6 mm uncoated carbide and HSS drill bits using a CNC machine under dry conditions and different drilling parameters. The characteristics of the hole quality are investigated in terms of its perpendicularity, cylindricity, circularity and hole size. An ANOVA (analysis of variance) and Pareto charts are used to analyze the effects of the drilling parameters on the hole quality. The hole quality is also assessed using a digital microscope to observe the formation of hole burrs. Moreover, scanning electron microscopy is also used to investigate the inside-hole surface defects. Further investigations are carried out using optical microscopy to inspect the post-drilling tool condition at high drilling parameters. The results show that hole quality reduces as the feed rate and spindle speed increase. However, from the ANOVA results and Pareto charts, the influence of the feed rate on the hole quality is found to be insignificant. At the same time, the type of drill bit material shows the highest percentage of contribution affecting the hole quality, following the spindle speed. The HSS drill bit shows more adhesion and built-up edges than the uncoated carbide drill bit. There were more burrs formed at the hole edges when the holes were drilled with uncoated HSS drill bits. In the same way, the SEM analysis reveals more surface deformation and damage defects inside the hole walls of holes drilled using the uncoated HSS drill bit.

Novel crack repair method of steel bridge diaphragm employing Fe-SMA

To repair cracks at the arc-shape cutouts of the diaphragm in the orthotropic steel deck (OSD) bridges, the Fe-SMA plates covering crack-stop holes method is proposed. Bonding the activated Fe-SMA plate can effectively reduce the stress level of the cracked region by increasing the local stiffness and introducing precompression. The recovery stresses of Fe-SMA with the pretension strain of 4% and activation temperatures of 150 °C, 200 °C, and 250 °C are 192.3, 226.4, and 270.8 MPa respectively, which can meet the requirements for crack reinforcement of engineering structures. To reinforce the diaphragms, compression stresses of 44.2–63.9 MPa are introduced at the hole edge after activating Fe-SMA, considerably reducing the local stress amplitude and stress concentration. The activating operation by heating has little effect on the bonding performance between the Fe-SMA plate and the diaphragm. The fatigue notch factor is reduced by 66.36% by bonding the Fe-SMA plate, and can be further reduced by about 14% after activating Fe-SMA. Additionally, the practical reinforcement application on the cracked diaphragm cutouts of the Sutong Bridge has confirmed the feasibility and efficacy of the novel Fe-SMA plates covering crack-stop holes method.

A Numerical Evaluation of Forming Failure of an Aluminum Sheet due to Splitting Damage in Hole Expansion Process

Abstract The reduction of car body weight is the principal issue of car manufacturers for reducing fuel consumption. Aluminum alloys are attractive materials for the automotive industry because they have low density and adequate strength, but they may exhibit crack formation during manufacturing processes. Generally, crack formations emerge because of tool geometry and material anisotropy. Accordingly, determination of the forming limits of aluminum alloys is essential. The hole expansion test (HET) is a significant formability process used in the automotive industry because it gives information about the stretch-flangeability limits of the material. Edge splitting (edge fracture) is a failure type seen in HET, and it limits the stretch-flangeability of the material. Therefore, the prediction of edge splitting is an essential issue for engineers in the automotive industry. In this work, HET of AA6016-O aluminum alloy was simulated with the finite element (FE) method to assess the influence of yield functions on failure prediction in HET. To this end, Hill48, Yld91, and a homogeneous fourth-order polynomial type yield criteria (HomPol4) were selected to identify the anisotropic behavior of the sheet. Analyses were carried out in Marc commercial FE software, and the Hypela2 user subroutine was incorporated into FE code. Thickness distributions in the rolling direction (RD), diagonal direction, and transverse direction (TD) of the part and around the hole edge were also predicted, and it was observed that only the HomPol4 criterion predicted excessive thinning at two locations near the RD and TD, separately. On the other hand, Yld91 and Hill48 predicted lower strain levels when compared with HomPol4. Finally, plastic work distribution around the hole edge was considered, and the predictions were compared with the experimental damaged sample. This comparison showed that HomPol4 predicted a robust plastic work localization in RD, which is consistent with the damaged sample.

A novel hybrid flux finite element model to steady heat conduction in porous materials

A new hybrid finite-element model was developed for heat flux and temperature analyses in porous material. The model in this paper was based on an assumed heat flux hybrid finite-element method, which is a two-field functional. An independent heat flux field that meets a priori inner thermal equilibrium was assumed inside the element, and a temperature field was assumed on the cell boundary. Temperature was used as the Lagrange multiplier to introduce the continuous condition of heat flux at the hole edge into the functional, and a modified complementary energy functional was obtained. The element flux field that was built up of polynomial terms and reciprocal terms from the stream function and that can consider the shape of pores in location coordinates was raised for the first time. Several numerical examples are discussed and compared with conventional finite-element methods to validate the accuracy and efficiency of the proposed approach.

Design for the Vent Holes of Gas Turbine Flow Guide Disks Based on the Shape Optimization Method

Two shape optimization methods, based on non-parametric and geometric parameters, were developed to address stress concentrations in the vent holes of gas turbine flow guide disks. The design optimization focused on reducing the maximum equivalent stress at the hole edge in an aero-engine gas turbine flow guide disk. The effectiveness of both methods in achieving this objective was studied. The results indicated that the non-parametric-based optimization method reduced the maximum equivalent stress at the hole edge by 24.5% compared to the initial design, while the geometric parameter-based optimization method achieved a reduction of 20.2%. Both shape optimization methods proved effective in reducing stress concentrations and improving fatigue life. However, the non-parametric shape optimization method resulted in a better design for the vent holes based on the study’s findings.

Mechanical properties of 3D 4-directional braided composites with a central circular hole under tension

3D braided composites are suitable for components that are prone to stress concentration owing to their low delaminating tendency and high damage tolerance. However, there are few researches that have investigated the mechanical properties of the braided composites with holes in multi-scale. In this article, an analysis method is proposed for the mechanical properties of 3D 4-directional braided composites with a central circular hole. The macro equivalent stiffness of the composites is calculated by homogenization method. Based on the modified Lekhnitskii theory, the transverse and tangential stresses at the hole edge of braided composite plates are attained. The models of meso unit cells with different braided angles are established, and the strength of the composites is predicted by Tsai-Wu criterion. The point stress criterion, the average stress criterion, and the progressive damage analysis method on the basis of different failure criteria are adopted to study the tensile strength of the braided composite plates with a hole, respectively. The study of mechanical properties of 3D 4-directional braided composites with a circular hole under tension in the article provides theoretical and simulation methods for such problems in engineering.

Progressive damage analysis and experiments of open-hole composite laminates subjected to compression loads

Due to the stress concentration caused by the hole, failure of composite structures is prone to start in the vicinity of the hole edge. Thereby, it is very necessary to investigate the failure of open-hole composite laminates. In the present work, a user subroutine element in the commercial software ABAQUS is proposed for the progressive damage analysis of open-hole composite laminates subjected to compression loads. The proposed element is constructed by making use of the third-order shear deformation theory in conjunction with a two-dimensional progressive damage model. The fiber kink model and Puck criterion are introduced for failure analysis of fiber and matrix, respectively. The element weakening method is also utilized to predict the damage evolution of open-hole composite laminates subjected to compression loads. To verify the reliability of the proposed model, the compression tests of open-hole composite laminates have been carried out. The percentage error of failure load predicted by the proposed element relative to the experimental result is 6.1%. Furthermore, the proposed element presents the damage evolution of fiber and matrix for the lamina with different stacking angles. It is observed that the fiber and matrix damage occurs firstly at the hole edge for the 45 and 0 degree plies, and the damage propagates along the 45 degree direction. This method can contribute to exploring the failure mechanism of open-hole composite laminates, which can also serve as a reference for the design of composite structures.

Edge fracture of the first and third-generation high-strength steels: DP1000 and QP1000

Advanced high-strength steels (AHSS) have shown profound progress in improving tensile ductility or global formality in the last decades over three generations. For a complete assessment of both the global and local formability, this study aims to characterize and compare the tensile and edge fracture behavior of the first and third-generation AHSS (dual-phase steel and quenching & partitioning steel) with the same nominal strength level of 980 MPa. Uniaxial tensile tests are performed to characterize the tensile properties. Hole expansion tests are conducted with two edge conditions based on separated preparation techniques (waterjet with polishing and punching) to investigate the edge fracture for both materials. The hole expansion ratios and edge fractures are compared between two materials and two edge conditions. It is concluded that the investigated QP1000 has promoted global formability while the DP1000 shows better local formability due to its damage-tolerant and crack-resistant responses.

Online active and dynamic object shape exploration with a multi-fingered robotic hand

The sense of touch can provide a robot with a wealth of information about the contact region when interacting with an unknown environment. Nevertheless, utilizing touch information to plan exploration paths and adjust robot posture to improve task efficiency remains challenging. This paper presents a novel approach for the online tactile surface exploration of unknown objects with a multi-degree of freedom robotic hand. We propose an exploration strategy that actively maximizes the entropy of the acquired data while dynamically balancing the exploration’s global knowledge and local complexity. We demonstrate that our method can efficiently control a multi-fingered robotic hand to explore objects of arbitrary shapes (e.g., with a handle, hole, or sharp edges). To facilitate efficient multi-contact exploration with a robotic hand, we offer an optimization-based planning algorithm that adapts the hand pose to the local surface geometry online and increases the kinematic configuration of each finger during exploration. Ultimately, we compared our approach to state of the art in a simulated environment. Experimental results indicate that our proposed methods can guide a multi-finger robotic hand to explore efficiently and smoothly, thereby reconstructing the unknown geometry of a variety of everyday objects, with significant improvements in data efficiency and finger compliance when compared to state-of-the-art approaches.

Magnetic Sensor-Based Switching Cabinet Busbar Current Measurement Method

Traditional switchgear current measurement techniques use closed-loop current modules to accurately measure and control current, and in switchgear, there is also interphase interference, these modules usually require a large core that surrounds the entire busbar as well as a shielded shell, because the compensation current generated inside the module is proportional to the busbar current, so the power consumption can be as high as several watts. In view of this, this paper proposes a magnetic sensor-based switch cabinet busbar current measurement method, and through theoretical deduction, it is determined that the magnetic sensor with two magnetic sensitive directions opposite and vertically placed in the busbar can eliminate the interference from the busbar phase and the stray field. Through simulation analysis, it was determined that the opening hole of the switch cabinet bus row was a circular hole, and the placement of the two magnetic sensors was at the edge of the circular hole, so that the practical application of the method in the switch cabinet had certain guiding significance.

Effect of pre-fatigue damage on the residual strength of 2198-T8 aluminum-lithium alloy sheet with holes

The 2198-T8 aluminum-lithium alloy is the advanced aircraft aluminum-lithium alloy used for airframe construction. During the service of the aircraft, the rivet joints of the fuselage skin are vulnerable to fatigue damage, which is accompanied by the formation of fatigue cracks near the rivet holes. The influences of pre-fatigue damage on the residual strength of 2198-T8 aluminum-lithium alloy with rivet holes were studied by combining the digital image correlation (DIC) technique and the micro and macro fracture morphology. The results show that with the increase of the pre-fatigue loading ratio, the residual strength and residual strain of 2198-T8 aluminum-lithium alloy gradually decrease, and when the pre-fatigue loading ratio is greater than 90 %, the attenuation trend is sharply accelerated. The relationship between residual strength and residual strain satisfies the residual strength degradation model, and the formula has a goodness of fit of 0.9878. The fatigue cracks at the hole edge propagate in both vertical and horizontal directions, and the propagation rate increases with the increase of the pre-fatigue loading ratio, and the fatigue striations gradually widen.

Numerical study of nozzle erosion in a hybrid rocket motor with wagon wheel fuel grain

Nozzle erosion directly affects the design quality of hybrid rocket motors, and it is a critical issue that restricts the practical application of hybrid rocket motors. In this paper, coupled numerical simulations of combustion flow field and thermochemical erosion of a graphite nozzle in a hybrid rocket motor with multi-port wagon wheel fuel grain are carried out. The results indicate that distributions of temperature, species and erosion rate in the flow field of hybrid rocket motor with wagon wheel grain show symmetrical characteristics related to the grain shape. The erosion rate decreases at first and then increases at the convergent section of throat insert, and it reaches the maximum value at the transition arc between convergent section and straight section of the throat. The maximum erosion rates at the central hole (position A) and outer edge of wheel holes (position B) are 0.0625 mm/s and 0.0902 mm/s, respectively. The erosion rate increases slowly in the straight section of the throat and it decreases gradually in the divergent section. Circumferentially inhomogeneous ablation occurs in the throat, and the erosion rate at the front end of throat straight section varies from 0.0484 mm/s to 0.0809 mm/s. The main oxidizing species causing thermochemical erosion are H2O and OH. At position A in the front end of throat straight section, erosion rates caused by H2O and OH are 66.50% and 30.48%, respectively. With the increase of oxidizer mass flow rate, the combustion chamber pressure increases linearly, and the erosion rate at position A in the front end of throat straight section gradually increases, but the growth rate decreases.

Soundness Evaluation for Edge of Round Hole Opened in Plate Using Second Harmonic Lamb Waves

Soundness Evaluation for Edge of Round Hole Opened in Plate Using Second Harmonic Lamb Waves

Parametric finite element analysis of laminated coupling

AbstractTo systematically and efficiently study the relationship between the design parameters and the strength and performance of the laminated coupling, it is expected to provide a theoretical basis for the design and selection of the coupling. Based on ANSYS parametric design language, parametric modeling and analysis were carried out on four different types of membranes, namely circular, multilateral, joint and plum‐pattern membranes. The loads and constraints were parameterized and the automatic grid division and analytical parameter control were realized, so as to obtain the stress distribution rule of the membranes. Based on Python language and parameterized commands, the secondary development of the membrane parametric finite element analysis tool was provided. The influence law of the factors such as angular displacement, torque, thickness, and the number of holes on the membrane performance was studied respectively, so as to achieve efficient finite element analysis. Results show that stress concentration exists near the hole edge of the membranes under the action of torque and angular displacement. Both the increase of torque and angular displacement will maximize the equivalent stress of the membranes, and appropriately reducing the thickness of the single membrane can lower the equivalent stress of the membranes.

Investigation of mechanical properties and elucidation of factors affecting wood-based structural panels under embedment stress with a circular dowel i: analysis of the influence of various conditions on the embedment properties

Embedment properties are vital to timber structural designs, and many types of wood-based structural panels have been developed for diverse uses. Comprehensive and systematic studies regarding the embedment properties of wood-based structural panels are limited. In this study, a jig that allows the observation of fracture processes is developed, and a monotonic tensile embedment test is conducted on plywood, oriented strandboard (both strong and weak axes), particleboard, medium density fiberboard, and hardboard. The parameters used in the test are the dowel diameter, pilot hole size, and end and edge distances. The effects of these parameters on the embedment properties (i.e., the failure mode, ductility, maximum stress, and yield stress) are discussed comprehensively. The failure mode is determined by the edge distance. At a sufficient edge distance, ductile failure occurs, and the load is maintained until the remaining end distance reaches a certain value. The maximum stress and yield stress are analyzed quantitatively via standardized multiple regression analysis. The results suggest the following: (i) The ratio of the in-plane strength to the internal bond strength is related to the failure behavior; (ii) the dowel diameter, fiber direction, and load levels affect the stress spread pattern of the embedment pressure.